In a typical electric starter motor, for instance, one for starting an automobile engine, there is a pinion that is moved into an engagement position on the engine flywheel. A particularly common starter of this type has an electrically operated solenoid to move a lever to slide a pinion assembly along the armature shaft, causing the pinion to engage the flywheel teeth. The pinion assembly normally consists of a clutch, its purpose being to prevent motor overloading and reverse driving when the engine starts.
The pinion assembly most typically moves within a cylindrical housing on the end of the starter housing; and part of this housing is cut-away area exposing the pinion gear. The engine flywheel extends into this cut-away portion, making it possible for the pinion gear to be moved into the position engaging the flywheel.
The opening in the housing for the flywheel provides a clear path for liquid, dust and particulate matter to the interior of the starter. Such contaminating materials ultimately cause premature wear of the electric motor, especially the bearings and commutator brushes. Specifically, contaminating material enters through the open annular space between the pinion assembly and the case. This contamination problem is especially serious when the electric starter motor is vertically oriented as are some starter motors. In this application, particulate easily settles on and around the pinion assembly. Because the pinion assembly moves abruptly, the particulate has a greater (natural) tendency to fall into the interior of the starter.